1. Field of the Invention
The present invention relates to an apparatus for managing dynamic bandwidth allocation that may be implemented in an optical line terminal (OLT), to support a low-power mode of an optical network unit (ONU) in a passive optical network (PON) system.
2. Description of the Related Art
Efforts to prevent CO2 emissions caused by global warming have been made globally. A green information technology (IT) based on ‘green of IT’ and ‘green by IT,’ is emerging as an important factor in research and development of IT.
Due to such a historical background, in an international telecommunication union-telecommunication standardization sector (ITU-T) SG15, G.sup45 was prepared on May, 2009, a gigabit passive optical network (GPON) power saving mechanism has been adopted as a baseline, and a low-power support scheme to be inserted in a standard draft of a 10-gigabit (XG)-PON1 has been discussed in detail in a full service access network (FSAN).
Additionally, a GreenTouch, namely a global consortium for improvement of a communication energy efficiency, is conducting researches to develop a technology for improving an energy efficiency by 1,000 times more than a current energy efficiency, which is led by Bell Labs that is the Alcatel-Lucent's research and development (R & D) organization.
A power saving scheme recommended by an XG-PON1, namely a standard of a next generation optical network of the ITU-T, is broadly classified into a dozing mode and a cyclic sleep mode. The dozing mode may refer to a scheme that needs to be applied in the power saving scheme for the XG-PON1 and that enables an optical network unit (ONU) to be switched to a power saving mode based on a trigger of an optical line terminal (OLT) or the ONU when there is no traffic received to a user network interface (UNI) and an access network interface (ANI) of the ONU.
A scheme of operating an ONU in the power saving mode may reduce power by deactivating an operation of an optical transceiver (OTRx), an XGPON media access control (MAC), an Ethernet switch, and the like that are included in the ONU. However, the dozing mode and the cyclic sleep mode may periodically deactivate only an optical signal transmission interface, instead of deactivating an optical signal reception interface of the ONU (an Rx of the OTRx).
Additionally, since an OLT continues to maintain a bandwidth allocated when an initial ONU is connected, while the ONU is operated in the power saving mode, an energy consumption efficiency of an Rx block of the XGPON MAC connected to the optical signal reception interface may be substantially the same as before the power saving mode.
Accordingly, since bandwidth allocation for upstream transmission of an ONU is equally performed in a normal mode, instead of the power saving mode, ONUs in the power saving mode may not respond to the bandwidth allocation. Thus, an OLT may detect an upstream transmission error of a corresponding ONU.
In addition, since a restricted upstream transmission bandwidth is used as a target of a dynamic bandwidth allocation algorithm for upstream bandwidth allocation, without distinguishing ONUs operated in the power saving mode from ONUs operated in the normal mode, an upstream transmission bandwidth may be wasted due to ONUs in the power saving mode in which upstream transmission is not performed actually, and accordingly the restricted upstream transmission bandwidth may be inefficiently used.